A number of microorganisms belonging to the genera of algae, yeast, bacteria, and fungi have ability to accumulate neutral lipids under specific cultivation conditions. The microbial lipids contain high fractions of polyunsaturated fatty acids and have the potential to serve as a source of significant quantities of transportation fuels. This paper reviews the current state of the art of this field. It summarizes the various microorganism used, feed stocks available, environmental factors that influence growth of cells and accumulation of lipids, major fatty acid composition of lipids, and the technology.

Municipal wastewater treatment plants in the USA produce over 6.2 · 10 6 t of dried sewage sludge every year. This microorganism-rich sludge is often landfilled or used as fertilizer. Recent restrictions on the use of sewage sludge, however, have resulted in increased disposal problems. Extraction of lipids from sludge yields an untapped source of cheap feedstock for biodiesel production. Solvents used for extraction in this study include n-hexane, methanol, acetone, and supercritical CO 2 . The gravimetric yield of oil was low for nonpolar solvents, but use of polar solvents gave a considerably increased yield; however, the percentage of saponifiable material was less. Extraction of lipids with a mixture of n-hexane, methanol, and acetone gave the largest conversion to biodiesel compared with other solvent systems, 4.41% based on total dry weight of sludge. In situ transesterification of dried sludge resulted in a yield of 6.23%. If a 10% dry weight yield of fatty acid methyl esters is assumed, the amount of biodiesel available for production in the USA is 1.4 · 10 6 m 3 /year. Outfitting 50% of municipal wastewater plants for lipid extraction and transesterification could result in enough biodiesel production to replace 0.5% of the national petroleum diesel demand (0.7 · 10 6 m 3 ).

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This chapter provides a brief overview of role of algae for the production of fuels and chemicals. Characteristics of algae and its production in open raceway ponds have been covered to identify the critical areas that require further exploration and development.

A large amount of alligator fat (AF) is produced by alligator meat processing industry and disposed in landfills or discarded as waste. The AF can be used as a potential feedstock for biodiesel production due to its high lipid content. In this work, recovery of lipids from the AF tissue was studied by solvent extraction as well as by microwave rendering. Microwave rendering resulted in AF oil recovery of 61% by weight of the frozen AF tissue obtained from producers. The fatty acid profile of the lipid showed that palmitic acid (C16:0), palmitoleic acid (C16:1), and oleic acid (C18:1) were the dominant fatty acids accounting for 89–92% of all lipids by mass; 30% of the fatty acids were saturated and 70% were unsaturated. The biodiesel produced from AF oil was found to meet the ASTM specifications of biodiesel concerning kinematic viscosity, sulfur, free and total glycerin, flash point, cloud point, and acid number.